This invention provides a vaccine for protecting an avian against an avian pathogen such as Infectious Bursal Disease Virus, Newcastle Disease Virus, or Mycoplasma gallisepticum, which comprises an effective immunizing amount of a vector comprising an isolated nucleic acid encoding Infectious Bursal Disease Virus peptides such as VP1, VP1s1, VP1s2, VP2, VP2S, VP3, VP4, VP4S and VP5, and a suitable carrier. Further, this invention provides a method for enhancing an avian immune response which comprises administering to the avian an effective amount of the vaccine and a method of immunizing an avian comprising administrating to the avian an effective amount of the vaccine.
Infectious bursal disease (IBD) has been observed in chickens since 1957. Birds which survive the disease are permanently immunosuppressed. Therefore they are more susceptible to other disease causing agents and do not respond adequately to vaccinations which are an essential part of poultry management systems. The bursa of Fabricius (BF) is the primary target organ of IBDV. The virus replicates in immature bursa-derived lymphocytes (B-lymphocytes) of chickens. Chickens infected with IBDV at one day of age are completely devoid of serum immunoglobulin G (IgG) and produce only monomeric IgM. A permanent decrease in the number of peripheral blood B cells was observed following an IBDV infection.
Infectious bursal disease virus (IBDV) causes immunosuppression of the humoral immune system of young chickens. Antibodies produced as a result of an IBDV infection will protect birds from the disease. Thus, control of this disease is achieved by vaccination with live-attenuated viruses. Diagnosis of IBDV is accomplished using assays such as immunofluorescence and antigen capture ELISA, which can detect presence, but not identify serotype, antigenic subtype or virulence of the virus. In some strains of the virus they constitute 50 and 50% of the virus protein respectively. Neutralizing epitopes were detected on VP2 and VP3. Antibodies to these epitopes were found to passively protect chickens (Azad et al. Virology m pp 145-153 1987). Several attempts were made to produce recombinant vaccines. VP2 expressed in E. coli failed to promote neutralizing antibodies in chickens. However when expressed in yeasts VP2 conferred protection (Macreadie and Azad Vaccine S pp 549-552 1990). The production of large amounts of recombinant VP2 in a baculovirus expression system was shown to protect chicken against disease (Pitcovski et al. Avian Diseases 40: 753-761 1996).
An effective IBD prevention and control program must involve an effective breeder vaccination program, an effective biosecurity program, and an effective broiler vaccination program. Immunization of breeders is an important part of the IBD control program. Antibodies produced by the hen are passed through the egg to the broiler chick. These maternal antibodies, if present in adequate levels, protect the chicks against subclinical IBD. An example of a comprehensive breeder vaccination program where subclinical IBD is a problem might have a vaccine schedule such as this: at 12 to 15 days of age IBD live; at 30 to 33 days of age IBD live; at 85 days of age IBD live or inactivated; and at 120 days of age IBD inactivated. Revaccinate at 38 to 42 weeks of age with an inactivated IBD vaccine if breeder titers are low or of poor uniformity. Routinely monitor breeder IBD antibody titers to ensure vaccines are administered properly and that the chickens respond appropriately.
Three categories of vaccines, based on their pathogenicity, have been described: 1) mild, 2) intermediate, and 3) virulent. The intermediate type IBD vaccines are most commonly used. These vaccines can stimulate the broiler to produce antibodies earlier than the mild-type vaccines, without significant damage to the BF as may occur with the virulent type vaccines. The timing of broiler vaccination depends on the level of maternal antibody present in the chicks. High levels of maternal antibody at the time of vaccination will neutralize the vaccine virus. Thus, only a limited active immune response results, and chickens will be susceptible to disease as maternal titers decrease. If low levels of maternal IBD titers are present in the chicks, vaccination may not be effective on farms contaminated with virulent field virus. Approximately 10 to 12 days are required after vaccination for chickens to develop minimal protective titers. During this xe2x80x9clag time,xe2x80x9d chickens are susceptible to IBD. Hence, the advantage of a vaccine that can be given in the presence of maternal antibodies.
In addition, virulent IBD viruses are able to break through higher maternal titers than milder vaccine viruses. Thus, if IBD field virus contamination on a broiler farm is high, nor broiler vaccination can stimulate protection in the flock before damage occurs. If the maternal antibody titer is not uniform in the broiler flock, multiple costly vaccinations will be required. For example, some producers may vaccinate broilers at one day of age and again at fourteen days of age. This multiple IBD vaccination would be recommended when maternal titers are poorly uniform, which results from poor vaccine administration in breeders or when mixing broilers from different breeder flocks. In a recent study, even a group of breeders that had fairly uniform IBD titers had chicks with titers that were variable, with many chicks have little or no maternal antibody protection. Although the 1 day of age vaccination would be of little direct benefit to broilers with high maternal titer levels, multiple vaccinations would provide some protection to chicks with lower levels of maternal antibody and would help reduce replication of IBD field virus and subsequent shed in the poultry house environment.
IBDV is highly contagious and can spread quickly through a flock. Infection is distributed through contaminated feed and water. The disease is commonly diagnosed in birds between 3 and 6 weeks old. Gross lesions can be seen for the most part on the bursa of Fabricius. The bursa may be swollen, or show signs of hemorrhage. In some cases, however, no lesions are observed and the bursa shrinks in size. Chickens with the disease exhibit anorexia, depression, watery diarrhea, ruffled feathers, soiled vent feathers, vent picking, and death. The course is usually 5-7 days. Protection of chickens from IBD through the use of vaccines is complicated by the presence of two serotypes and several antigenic subtypes of the virus. Vaccination with a given antigenic subtype of IBDV serotype I will not always protect chicks from the disease when the challenge virus is a different antigenic subtype.
It is possible to alter cells in a selected way by putting foreign DNA into them. It was shown already at the mid 1950S that cells could take up nucleic acids extracted from viruses and express them as proteins. Since then efforts were directed to improve the efficacy of the deliveryxe2x80x94transfectionxe2x80x94of functional genes to cells. The main obstacle to DNA uptake was thought to be the negative electrical charge of the nucleic acid. The DNA molecule is repelled from the membranes of the cells because they are negatively charged. Techniques were developed to neutralize the DNA, negative charge, among them is the treatment with calcium phosphate or DEAE dextran.
Advances in the field of DNA transfection took place with the development of recombinant DNA technique. It allowed the insertion of individual genes from cells into plasmids. The delivery of the recombinant plasmids derived from the bacteria into cultured eucaryotic cells allowed the expression of the inserted genes and the production of recombinant proteins in the cell at will. Industry has made use of the technique to produce a growing list of recombinant proteins of medicinal value like insulin, factor VIII, growth factors and cytokines. Advances in the field of DNA transfectionxe2x80x94including the development of gene carrying liposomesxe2x80x94lipid micelles xe2x80x9cloadedxe2x80x9d with recombinant plasmids brought about hopes that the technique may be applied for gene therapyxe2x80x94the introduction into the body of genes that produce proteins of therapeutic value. It is not clear yet whether this approach can bring about the in vivo expression of therapeutic amounts of the recombinant protein, but at the neater term it seems to have promise for use in vaccines. Even minute amounts of protein can stimulate a protective immune response against infectious agents parasites.
In the last three years, DNA vaccines have burst onto the scene as radically new like viruses, bacteria and approach to infectious disease prophylaxis. One of the most surprising and important features of DNA immunization is that purified xe2x80x9cnakedxe2x80x9d DNA appears to be taken up and expressed by cells in vivo with much greater efficiency than would have been. Not much has been reported in the field of chicken infectious diseases. A report on the protection of chicken against a lethal influenza virus challenge with plasmid DNA by Robinson et al. (Vaccine vol. 1 pp 957-960 1993) opened the avenue for the improvement of protective efficacy in chicken. Chicken injected intramuscularly twice with plasmid DNA expressing heamagglutinin (HA) were protected from lethal challenge with a virulent influenza virus. A more recent work from the same group (Kodihalli et al. J. Virol. Vol 71 pp 3391-3396 1997) shows that the HA DNA vaccine conferred 95% cross-protection against challenge with lethal antigenic variants that differ from the primary antigen by 11 to 13%. Several attempts were made to produce recombinant vaccines. VP2 expressed in E. coli failed to promote neutralizing antibodies in chickens. However when expressed in yeasts VP2 conferred protection (Macreadie and Azad Vaccine S pp 519-552 1990). Production of recombinant VP2 using the baculovirus expression system (Piteovski et al. Avian Diseases 40: 753-761 1996 and Goodwin M A et al. Vaccine 1994 12 452-456 1994.) has been reported.
This invention provides a vector comprising one or more isolated nucleic acids encoding an infectious bursal disease virus polypeptide, or a mutant or variant thereof, wherein said nucleic acid is under the control of a promoter. This invention provides a vector comprising one or more isolated nucleic acids encoding an infectious bursal disease VP1, VP1s1, VP1s2, VP2, VP2S, VP3, VP4, VP4S and VP5 or a mutant or variant thereof, wherein said nucleic acid is under the control of a promoter.
This invention provides a vaccine for protecting an avian against an avian pathogen such as Infectious Bursal Disease Virus, Newcastle Disease Virus, or Mycoplasma gallisepticum, which comprises an effective immunizing amount of a vector comprising 1) one or more isolated nucleic acids encoding an infectious bursal disease virus polypeptide, or a mutant or variant thereof, wherein said nucleic acid is under the control of a promoter; and 2) a suitable carrier and/or adjuvant.
This invention provides a vaccine for protecting an avian against an avian pathogen such as Infectious Bursal Disease Virus, Newcastle Disease Virus, or Mycoplasma gallisepticum, which comprises an effective immunizing amount of a vector comprising 1) one or more isolated nucleic acids encoding an infectious bursal disease VP1, VP1s1, VP1s2, VP2, VP2S, VP3, VP4, VP4S and VP5, or a mutant or variant thereof, wherein said nucleic acid is under the control of a promoter; and 2) a suitable carrier and/or adjuvant. Further, it is contemplated that the vaccine comprises a mixture of VP2 and VP2s.
This invention provides a method for enhancing an avian immune response which comprises administering to the avian an effective amount of the vaccine and a method of immunizing an avian comprising administering to the avian an effective amount of the vaccine.